Inevitable cognitive bias
To get to a correct diagnosis, clinicians must navigate a wide variety of inherent cognitive biases. For example, with Mr O, if you hadn’t realized from the referral that he might have had Parkinson disease, you had to overcome the impact of “anchoring,” the tendency to stick with your first diagnostic impression. You also had to overcome “availability bias,” the tendency to think that a diagnosis that readily comes to mind is likely to be the correct diagnosis.
For psychiatrists, major depression or dysthymia with somatic concerns is a diagnostic formulation that is commonly seen and readily comes to mind. Parkinson disease comes less readily to mind.
Cognitive biases are ubiquitous; they reflect the flow of nonconscious predictions we make, based on past experiences, as we move through the world. The influence of cognitive biases on diagnostic reasoning has been well described by Croskerry2 who has studied diagnostic errors in emergency department settings where physicians have to make quick decisions with little information about the patient and are forced to rely heavily on error-prone systems.1
In the case of Mr O, it would have been a cognitive error to believe that the etiology of his symptoms was the difficulty he was having adjusting to retirement, along with his tendency to focus on somatic concerns. This would have been an “attribution error” in which you held the patient responsible for his or her disease. All physicians are prone to making attribution errors, especially when making a diagnosis in patients who have behavioral symptoms.
Another common bias is a tendency to look for confirming evidence—“confirmation bias”—rather than disconfirming evidence, although disconfirming evidence is much more powerful. It turns out that Mr O’s symptoms of restless sleep, constipation, fatigue, and depression actually began before he retired, not after.
Furthermore, it is helpful for clinicians to be aware of the possibility of “premature closure,” the tendency to stop investigating once you have come upon a diagnostic hypothesis but before that hypothesis has been fully proven. This is an especially easy error to make when a medical condition has a long prodromal period without symptoms that are specific enough to make a clear medical diagnosis. As psychiatrists, we often encounter diseases of this type; Parkinson disease is but one example. Others include: multiple sclerosis, Wilson disease, Alzheimer disease, Cushing disease, fronto-temporal dementia, Huntington disease, and more. Periodically reviewing a patient’s condition while maintaining diagnostic uncertainty forces the clinician to rely more on system 2 cognition.
Non-specific behavioral and mood alterations often represent the very first and, occasionally for prolonged periods of time, the one single and exclusive sign of an undetected physical illness. Flagrantly and convincingly “psychological” in nature on presentation, such masked physical conditions frequently mislead the examiner and obliterate any further medical consideration, resulting in misdiagnosis and thus, inevitably, in treatment gone astray.4
Recent studies of diagnostic error have not focused on patients who are being treated in mental health clinics or inpatient psychiatric units; however, past studies of psychiatric patients found that, important medical diagnoses were missed in these patients as often as 40% of the time, depending upon the setting.5 Moreover, these medical diagnoses were not uncommonly the sole cause or a significant contributing factor to the patients’ presentations.
Dr Schildkrout is Assistant Professor of Psychiatry, part time, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA. She is the author of two books: Unmasking Psychological Symptoms: How Therapists Can Learn to Recognize the Psychological Presentation of Medical Disorders and Masquerading Symptoms: Uncovering Physical Illnesses That Present as Psychological Problems.
1. Ball J, Balogh E, Miller BT, Eds. Improving Diagnosis in Health Care. Washington, DC: National Academies Press; 2015.
2. Croskerry P. The importance of cognitive errors in diagnosis and strategies to minimize them. Acad Med. 2003;78:75-780.
3. Croskerry P. Clinical cognition and diagnostic error: applications of a dual process model of reasoning. Adv Health Sci Ed. 2009;14:27-35.
4. Yates BL, Koran LM. Epidemiology and recognition of neuropsychiatric disorders in mental health settings. Ovsiew F, Ed. Neuropsychiatry and Mental Health Services. Washington, DC: American Psychiatric Press; 1999: 23-67.
5. Koranyi EK. Morbidity and rate of undiagnosed physical illness in a psychiatric clinic population. Arch Gen Psychiatry. 1979;36:414.
6. Schildkrout B. Complexities of the diagnostic process. J Nervous Mental Dis. 2018;206:488-490.
7. Schildkrout B. Masquerading Symptoms: Uncovering Physical Illnesses That Present as Psychological Problems. New York: John Wiley & Sons; 2014.